**Problem**Two blocks of masses

*m*

_{1}and

*m*

_{2}, with

*m*

_{1}>

*m*

_{2}, are placed in contact with each other on africtionless, horizontal surface, as in Active Figure 4.13a. Aconstant horizontal force = 118 N is applied to

*m*

_{1}asshown.

**(a)**If

*m*

_{1}= 15 kg and

*m*

_{2}= 10 kg, find themagnitude of the acceleration of the system of two blocks.

**(b)**Determine the magnitude of the contact force between thetwo blocks.

**(c)**Imagine that the force in Active Figure 4.13is applied toward the left on the right-hand block of mass

*m*

_{2}. Is the magnitude of the force

_{12}the sameas it was when the force was applied toward the right on

*m*

_{1}?

## Answers ( 2 )

Assume F

_{1 }= 118 N thenF_{1}= (m1 +m2) aa = F

_{1}/ (m1 + m2) = 118 / (10 + 15) = 4.72m/s^{2 }_{2}= the force exerted on m2 by m1_{2}= m2 a =10(4.72) = 47.2 N^{2}. Sothe force exerted on m1 by m2 is_{3}= m1 a =15 (4.72) = 70.8 N_{ }_{1 +}m_{2})b) m

_{1}a = F_{1}m_{2}a =F_{2 c) }F = m_{2}a